Movement sensitivities of cells in the fly's medulla

Summary

Intracellular recordings were made in the medullae of intact, restrained females ofCalliphora vicina that faced a hemispherical, minimum-distortion surface upon which moving patterns and spots were projected from the rear (Fig. 2). In the distal medulla, noisy hyperpolarizations to light, most likely recorded in terminals of laminar (L) cells, had flicker-like oscillations to moving gratings of 15° spatial wavelength but not of 2.5° spatial wavelength (Fig. 3). Medullary (M) cells penetrated distally responded to grating movements with similar but depolarizing oscillations, in one cell 180° out of phase with a nearby laminar response (Figs. 4–6).

A characteristic movement response recorded from most medullary cells consisted of abrupt, maintained nondirectional depolarizations in response to movements of gratings, often with directional ripple or spikes superimposed. When directions of movement reversed, there were brief repolarizations, but when movements stopped, depolarizations decayed away more slowly (Figs. 7 and 8). Magnitude of responses increased with increasing speeds of both 15° and 2.5° gratings (Figs. 9–11). In some cells, there were delayed decays of responses after stopping (Fig. 12). Still other cells seemed to receive inhibition from other, characteristically responding cells (Fig. 13).

Receptive fields tested were simple and usually large, with only a suggestion of surround inhibition (Fig. 14). In general, intensity and position were interchangeable over a cell's receptive field (Figs. 15 and 16). Moving edges and dark spots elicited responses primarily within receptive field centers (Figs. 18–20).

It is argued that waveforms of characteristic movement responses can be explained by multiplicative inputs from L- and M-cells to movement detectors (Figs. 21–26).